This invention relates to a belt stretcher that can be downsized, and a color image formation apparatus incorporating the same, in particular to a so-called tandem color image formation apparatus for transferring toner images formed by a plurality of single-color toner image formers in sequence to a belt or a recording medium held on the belt, thereby forming a color image.
Generally, each toner image former has a photoconductor having a photosensitive layer on the outer peripheral surface, a charger for uniformly charging the outer peripheral surface of the photoconductor, an exposer for selectively exposing the outer peripheral surface charged uniformly by the charger for forming an electrostatic latent image, and a developer for giving toner to the electrostatic latent image formed by the exposer for providing a visible image (toner image).
The known tandem image formation apparatus for forming a color image is of the type wherein a plurality of (for example, four) toner image formers as mentioned above are placed for an intermediate transfer belt and toner images on photoconductors provided by the single-color toner image formers are transferred to the intermediate transfer belt in sequence for superposing the toner images of a plurality of colors (for example, yellow, cyan, magenta, and black) on the intermediate transfer belt, thereby providing a color image on the intermediate transfer belt. Another known tandem image formation apparatus is of the type wherein a recording medium, such as paper, is held on a recording medium holding belt and toner images provided by a plurality of single-color toner image formers are transferred to the recording medium in sequence for superposing the toner images of a plurality of colors on the recording medium, thereby providing a color image on the recording medium.
The tandem color image formation apparatus of each type comprises a meander regulation (meander prevention) mechanism because a color shift occurs if the belt meanders.
An apparatus as shown in FIG. 10 is a related tandem image formation apparatus for forming a color image (disclosed in Japanese Patent Publication No. 3-191368A).
In this image formation apparatus, a plurality of (in this case, four) single-color toner image formers 101 (A, B, C, and D) are placed for an intermediate transfer belt 100.
Each single-color toner image former 101 has a photoconductor 102 having a photosensitive layer on the outer peripheral surface, a charger 103 for uniformly charging the outer peripheral surface of the photoconductor 102, an exposer 104 for selectively exposing the outer peripheral surface charged uniformly by the charger 103 for forming an electrostatic latent image, and a developer 105 for giving toner to the electrostatic latent image formed by the exposer 104 for providing a visible image (toner image).
The toner images on the photoconductors 102 provided by the single-color toner image formers 101 are primarily transferred to the intermediate transfer belt 100 in sequence by corona transfer devices 106 for superposing the toner images of a plurality of colors (for example, yellow, cyan, magenta, and black) in sequence on the intermediate transfer belt 100, thereby providing a color image on the intermediate transfer belt 100, and the color image is secondarily transferred from the intermediate transfer belt 100 to a recording medium P by a corona transfer device 110 in a secondary transfer section T2.
The recording medium P is supplied one at a time from a paper feeding cassette 107 by a paper feeding belt 108 and passes through gate rollers 109. In the secondary transfer section T2, a color toner image is transferred to the recording medium P. After then, the recording medium P is transported on an attractive transport belt 111. The color toner image is fixed by a fixing section 112 and the recording medium P is ejected onto a paper ejection tray 114 by ejection rollers 113.
Each single-color toner image former 101 is provided with a cleaning blade 115 for removing toner remaining on the surface of the photoconductor 102 after the toner image is transferred to the intermediate transfer belt 100, and the intermediate transfer belt 100 is provided with a cleaning blade 120 for removing toner remaining thereon after the secondary transfer.
The intermediate transfer belt 100 is placed on a drive roller 130 and a driven roller 131, and a tension roller 132 is placed on a slack side 100a of the intermediate transfer belt 100. A press roller 133 for pressing the intermediate transfer belt 100 against the photoconductor 102 is placed on a tense side 100b of the intermediate transfer belt 100.
The cleaning blade 120 abuts the intermediate transfer belt 100 in a winding part of the intermediate transfer belt 100 around the driven roller 131. Numeral 116 denotes a sensor for detecting a reference position of the belt.
The cleaning blade 120 acts on circulation of the intermediate transfer belt 100 as resistance. It acts as large resistance particularly when the drive roller 130 is activated (when circulating the belt is started).
In the related image formation apparatus, the cleaning blade 120 abuts the intermediate transfer belt 100 in the winding part of the intermediate transfer belt 100 around the driven roller 131 and thus the resistance of the cleaning blade 120 in the abutment part acts on the intermediate transfer belt 100 as a tensile force between the winding part and the winding part of the belt around the drive roller 130.
The abutment state of the cleaning blade 120 on the intermediate transfer belt 100 is not always stable because of the friction therebetween and becomes unstable particularly at the initial stage of driving. Therefore, in this stage, the tension acting on the intermediate transfer belt 100 between the drive roller 130 and the cleaning blade 120 also becomes unstable.
Therefore, the expansion and contraction state of the intermediate transfer belt 100 becomes unstable so that a shift between the transfer positions of color toner images onto the intermediate transfer belt 100 easily occurs. Consequently, the quality of a color image is easily degraded.
In this kind of color image formation apparatus, if the intermediate transfer belt meanders, a shift between colors occurs and thus it is desirable that a meander regulation (meander prevention) mechanism should be provided. In the apparatus as described above, the secondary transfer section T2 is formed in the winding part of the intermediate transfer belt 100 around the driven roller 131. Thus, it is undesirable that the driven roller 131 is used as a meander regulation roller. Since meander of the intermediate transfer belt is mainly regulated in the process from the winding start position of the intermediate transfer belt around the meander regulation roller to the winding end part, the intermediate transfer belt is easily displaced in the width direction thereof in the winding part and therefore the state of the secondary transfer easily becomes unstable.
Thus, in the apparatus as described above, the tension roller 132 or the press roller 133 needs to be used as a meander regulation roller.
However, in such a configuration, it is impossible to eliminate the tension roller 132 or the press roller 133 contrary to the requirement of simplification or downsizing of the apparatus. In addition, as seen in FIG. 10, the winding angle of the intermediate transfer belt 100 around the tension roller 132, the press roller 133 is small and thus it is hard to provide a sufficient meander regulation effect.
As a belt stretcher having a meander regulation mechanism, a mechanism as shown in FIG. 11 is known (disclosed in Japanese Patent Publication No. 5-52244A).
In the figure, a belt 3 is placed on a drive roller 1 and a driven roller 2 and circulated in the arrow A direction, with a driving force provided from a drive motor 4.
The driven roller 2 is provided as a regulation roller for regulating meander and at least one end 2c of the driven roller 2 is supported so that it can be moved in the arrow C direction for regulating meander.
The driven roller (regulation roller) 2 is provided at the end 2c with a tapered detection roller 5 (shaped like a truncated cone) that can be rotated independently of a roller main body 2b with respect to a shaft 2d, and a string member 7 wound around a boss part 5b of the detection roller 5 for joint is fixed to a frame S at an opposite end thereof.
Initially, the driven roller (regulation roller) 2 is placed so that as the axis-to-axis distance between the driven roller 2 and the drive roller 1, L2 on the side of a move end 2c is a little shorter than L1 on the side of a fixed end 2a and accordingly initially the belt 3 moves in the arrow B direction. However, when the belt 3 moves in the arrow B direction and an edge part 3a of the belt 3 is wound around a taper face of the detection roller 5, the detection roller 5 is rotated following the belt 3, whereby the string member 7 is wound around the boss part 5b of the detection roller 5 and is pulled and the free end 2c is pulled in the arrow C direction by reaction force and the above-mentioned axis-to-axis distance L2 on the move end 2c side becomes larger than the axis-to-axis distance L1 on the fixed end 2a side. Accordingly, the belt 3 moves in an opposite direction to the arrow B and consequently meander of the belt 3 is regulated.
According to such a belt stretcher, it is made possible to downsize the belt stretcher (and therefore downsize an image formation apparatus). That is, to regulate meander of a belt in a general belt stretcher, it is common practice to provide a third roller and implement the third roller as a meander regulation roller and thus at least three rollers are required, but the belt stretcher described with reference to FIG. 11 makes the third roller unnecessary and requires only two rollers, so that it is made possible to downsize the belt stretcher (and therefore downsize an image formation apparatus).
A belt less stretched to prevent a position shift of an image is used as a belt used with an image formation apparatus (for example, an intermediate transfer belt).
Thus, in fact, the belt stretcher in the related art shown in FIG. 11 is hard to provide the desired motion described above.
For example, to provide the desired motion described above, it is considered that the one end 2a of the regulation roller 2 is supported immovably and that only the opposite end 2c is supported movably in the arrow C direction. In doing so, however, it becomes difficult to give a predetermined tension to the belt 3, because the rollers 1 and 2, the belt 3, and the support members of the rollers 1 and 2 contain their respective dimension errors and an error also occurs in the axis-to-axis distance on the fixed end 2a side.
To make it possible to give a predetermined tension to the belt 3, for example, in FIG. 11, both the ends 2a and 2c of the regulation roller 2 may be urged (F1 and F2) initially by springs or the like, in the stretching direction of the belt 3 and the urging force F2 on the free end 2c side may be set a little smaller than the urging force F1 on the fixed end 2a side. However, to provide the desired motion described above, urging force F3 is required for urging the free end 2c of the regulation roller 2 in the former position direction (opposite to the arrow C direction) after the free end 2c moves in the arrow C direction.
However, in the belt stretcher shown in FIG. 11, the free end 2c of the regulation roller 2 moves in the initial stretching direction of the belt 3 (arrow C direction) and thus the urging force F3 cannot be set, because the urging force F3 and the urging force F2 cancel each other out. Therefore, the belt stretcher shown in FIG. 11 is hard substantially to provide the desired motion described above.
The problem described above can be solved by setting the moving direction of the regulation roller for meander regulation to any other direction than the initial stretching direction of the belt by the regulation roller.
In doing so, however, another problem arises as described below:
In a tandem color image formation apparatus, a plurality of single-color toner image formers are placed for a belt and toner images are transferred to the belt or a recording medium held on the belt. If the moving direction of the regulation roller for meander regulation is set to any other direction than the initial stretching direction of the belt by the regulation roller, the belt is displaced in a direction away from or close to the single-color toner image formers.
If the belt is displaced in the direction away from the single-color toner image formers, it is feared that the contact state between the belt and each toner image former (photoconductor thereof, for example) may become unstable in the transfer section, causing a transfer failure to occur.
If the belt is displaced toward the image formers, the winding angle of the belt with respect to the photoconductor, for example, in the toner image former closest to the regulation roller grows and the transfer bias fluctuates and thus it is still feared that a transfer failure may occur.
It is therefore a first object of the invention to provide a color image formation apparatus that can decrease a shift between the transfer positions of color toner images onto an intermediate transfer belt for enhancing the quality of a color image.
A second object of the invention to provide a color image formation apparatus that can lessen the number of rollers for downsizing the apparatus, and moreover can provide a sufficient meander regulation effect for consequently improving the image quality.
A third object of the invention to provide a color image formation apparatus that can provide a good transfer state although the moving direction of the regulation roller-for meander regulation is set to any other direction than the initial stretching direction of the belt by the regulation roller.
In order to achieve the above objects, according to the present invention, there is provided a color image formation apparatus, comprising:
a drive roller;
a driven roller;
a looped belt member, which is stretched by the drive roller and the driven roller and circulated therearound;
a plurality of image formers, each image former forms a toner image associated with each single color constituting a color image;
a plurality of transferring members, disposed on a circulating path of the belt member, each transferring member being associated with each image former for transferring the toner image onto either the belt member or a recording medium held on the belt member; and
a cleaning blade, abutted against a part of the belt member wound on the drive roller for removing toner remained on the belt member after the toner image transfer is performed.
In this configuration, since the cleaning blade abuts against the part of the belt member wound on the drive roller, the expansion and contraction state of the intermediate transfer belt becomes stable even at the initial stage of driving.
That is, as described above, the cleaning blade acts on circulation of the belt member as resistance and becomes large resistance particularly when driving is started. However, in the above configuration, the resistance of the cleaning blade in the abutment part cannot act as a tensile force of the belt member. It acts only on the winding part of the belt member around-the drive roller as resistance.
Thus, if the abutment state of the cleaning blade on the belt member is not stable because of the friction therebetween, the state does not affect any tension acting on the belt member.
Therefore, a shift between the transfer positions of color toner images onto the belt member or the recording medium is remarkably decreased even at the initial stage of image formation, and consequently the quality of a color image is enhanced.
Preferably, a friction coefficient of an outer peripheral surface of the drive roller is larger than a friction coefficient of an inner surface of the looped belt member.
In this configuration, the circulation of the belt member becomes further stable and therefore the expansion and contraction state of the belt member also becomes further stable.
Here, it is preferable that the drive roller serves as a secondary transfer member together with a secondary transfer roller in a case where the toner images are primarily transferred onto the belt member. A hardness of the outer peripheral surface of the drive roller is smaller than a hardness of the secondary transfer roller.
In this configuration, since a nip face in the secondary transfer section becomes a curved surface recessed to the side of the drive roller, a good strip property of the recording medium from the belt member in the secondary transfer section can be provided, and winding the recording medium around the belt member can be prevented.
Preferably, the driven roller serves as a regulation roller, which moves in a direction other than a direction in which the driven roller initially stretches the belt member to regulate meander action of the belt member.
In this configuration, since it is not necessary to provide any roller member other than the drive roller and the driven roller to regulate the meander action of the belt member, the apparatus can be downsized.
Here, it is preferable that the driven roller moves in a direction perpendicular to the initial stretching direction.
In this configuration, the meander action of the belt member can be regulated more efficiently. Moreover, it is made possible to fine regulation.
Alternatively, it is preferable that the driven roller moves in a direction such that a part of the belt member at which a transferring member closest to the driven roller is separated from the associated image former.
In this configuration, the winding angle of the belt member with respect to the image former does not grow and the fear of occurrence of a transfer failure is eliminated.
Therefore, a good transfer condition can be attained although the moving direction of the driven roller for meander regulation is set to any other direction than the initial stretching direction.
Here, it is preferable that the transferring member closest to the driven roller is provided as a transfer roller for urging the belt member toward the associated image former with an urging force greater than a force produced when the driven roller regulates the meander action of the belt member.
In this configuration, the contact state between the belt member and the image former becomes stable, causing no transfer failure to occur. Even if the urging force of the transfer roller is increased, the frictional force with the belt member does not grow and consequently a smooth running state of the belt member can be provided.
Further, it is preferable that the transferring members other than the transfer roller are provided as either transfer blades.
In this configuration, it is made possible to provide an inexpensive image formation apparatus with a simple structure as compared with the case where all transferring members are implemented as transfer rollers.
Alternatively, it is preferable that the color image formation apparatus further comprises a positioning member disposed between the driven roller and the transferring member closest to the driven roller, the positioning member being abutted against an inner surface of the looped belt member. Here, a friction coefficient of an abutting surface of the positioning member is less than a friction coefficient of the inner surface of the looped belt member.
In this configuration, even if the driven roller is displaced, the contact between the belt member and the toner image former becomes stable, causing no transfer failure to occur.
Since the positioning member has a good sliding proper relative to the belt member, the frictional force with the belt member does not much grow and consequently a smooth running state of the belt member can be provided.
Here, it is preferable that all of the transferring members are provided as either transfer blades or corona transfer devices.
In this configuration, since the need for implementing transfer rollers as the transferring members is eliminated, it is made possible to provide an inexpensive image formation apparatus with a simple structure.
Preferably, the drive roller serves as a secondary transfer member together with a secondary transfer roller in a case where the toner images are primarily transferred onto the belt member. Here, a diameter of the driven roller is larger than a diameter of the drive roller.
In this configuration, since the drive roller, which is a main factor member of causing meander to occur, has a smaller diameter than the driven roller, the meander distance itself of the intermediate transfer belt is decreased.
On the other hand, since the driven roller implemented as the meander regulation roller of the intermediate transfer belt has a larger diameter than the drive roller, and thus the winding length of the belt member is enlarged so that the meander of the belt member is regulated reliably and smoothly.
Therefore, the color image formation apparatus can provide a sufficient meander regulation effect and consequently the image quality is improved.
Further, meander regulation rollers other than the driven roller become unnecessary, so that it is made possible to downsize the apparatus.
Still further, the secondary transfer section is formed in the winding part of the belt member around the drive roller which is not the meander regulation roller, so that a stable secondary transfer state can be provided.
Moreover, the drive roller forming the secondary transfer section has a small diameter, so that the strip property of the recording medium from the secondary transfer section is improved and winding trouble of the-recording medium becomes hard to occur.
According to the present invention, there is also provided a color image formation apparatus, comprising:
a drive roller;
a driven roller;
a looped belt member, which is stretched by the drive roller and the driven roller and circulated therearound;
a plurality of image formers, each image former forms a toner image associated with each single color constituting a color image; and
a plurality of transferring members, disposed on a circulating path of the belt member, each transferring member being associated with each image former for transferring the toner image onto either the belt member or a recording medium held on the belt member, wherein:
the driven roller serves as a regulation roller, which moves in a direction other than a direction in which the driven roller initially stretches the belt member such that a part of the belt member at which a transferring member closest to the driven roller is separated from the associated image former, in order to regulate meander action of the belt member; and
the transferring member closest to the driven roller is provided as a transfer roller for urging the belt member toward the associated image former with an urging force greater than a force produced when the driven roller regulates the meander action of the belt member.
According to the present invention, there is also provided a color image formation apparatus, comprising:
a drive roller;
a driven roller;
a looped belt member, which is stretched by the drive roller and the driven roller and circulated therearound;
a plurality of image formers, each image former forms a toner image associated with each single color constituting a color image;
a plurality of transferring members, disposed on a circulating path of the belt member, each transferring member being associated with each image former for transferring the toner image onto either the belt member or a recording medium held on the belt member; and
a positioning member disposed between the driven roller and a transferring member closest to the driven roller, the positioning member being abutted against an inner surface of the looped belt member, wherein:
the driven roller serves as a regulation roller, which moves in a direction other than a direction in which the driven roller initially stretches the belt member such that a part of the belt member at which the transferring member closest to the driven roller is separated from the associated image former, in order to regulate meander action of the belt member; and
a friction coefficient of an abutting surface of the positioning member is less than a friction coefficient of the inner surface of the looped belt member.
According to the present invention, there is also provided a color image formation apparatus, comprising:
a drive roller having a first diameter;
a driven roller having a second diameter larger than the first diameter;
a looped belt member, which is stretched by the drive roller and the driven roller and circulated therearound;
a plurality of image formers, each image former forms a toner image associated with each single color constituting a color image;
a plurality of transferring members, disposed on a circulating path of the belt member, each transferring member being associated with each image former for primarily transferring the toner image onto the belt member; and
a secondary transfer roller, which urges the belt member toward the drive member to transfer the toner image on the belt member onto a recording medium placed therebetween.
According to the present invention, there is also provided a belt stretcher, comprising:
a drive roller;
a driven roller; and
a looped belt member, which is stretched by the drive roller and the driven roller and circulated therearound,
wherein the driven roller serves as a regulation roller, which moves in a direction other than a direction in which the driven roller initially stretches the belt member.
In this configuration, the urging force for urging the driven roller to the initial position after the meander regulation is not offset by the initial urging force for stretching the belt member. Since it is not necessary to provide any roller member other than the drive roller and the driven roller to regulate the meander action of the belt member, the apparatus can be downsized.